Question

A battery is marked. As having a voltage of 12V and is connected to a circuit that has a resistance of 5 ohms.if the terminal voltage is 8.75V. What is the internal resistance

Answer 1

1.857 Ohms

Step-by-step explanation:

The marked voltage of the battery is it's E.M.F. (Electromotive force). It is the maximum voltage the battery can supply because, ideally internal resistance of a cell or battery should be zero. Let us denote the E.M.F. as E.

In reality we get a lower voltage called the Terminal Voltage (Voltage across the terminals of the battery). Let us call that V. This is due to the voltage drop caused by the internal resistance (say 'r').

So when the circuit is connected a current I flows through a resistance

R(= 5 ohms, given).

Now, potential difference = Terminal Voltage = V = 8.75 Volts

Hence,
`I=(V)/(R) =(8.75)/(5)=1.75 Amperes`

Now, by conservation of energy we can say that,

E.M.F. = Terminal Voltage + Voltage drop due to the battery's internal resistance

or,
`E=V+Ir`

or,
`r=(E-V)/(I)=(12-8.75)/(1.75)=1.857` Ohms